Gear-changing mechanism for motor vehicles



June 1, 1937. R. c, CLERK 2,082,332

GEAR CHANGING MECHANISM FOR MOTOR VEHICLES Filed Oct. 20, 1954 15 Sheets-Sheet 1 55 58 25 54a 57 57 5 92 50 50 89 I 84 aoi I 53 June 1, 1937. R. c. CLERK 2,082,382

GEAR CHANGING MECHANISM FOR MOTOR VEHICLES Filed Oct. 20, 1934 15 Sheets-Sheet 2 June 1, 1937. R. c. CLERK 2,082,382

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GEAR CHANGING MECHANISM FOR MOTOR VEHICLES Filed Oct. 20, 1934 15 Sheets-Sheet 7 19/10 o n-y June 1, 1937. c, CLERK v 2,082,382

GEAR CHANGING MECHANISM FOR MOTOR VEHICLES Filed Oct. 20, 1934 15 Sheets-Sheet 8 2o Jeri June 1, 1937. R. c. CLERK GEAR CHANGING MECHANISM FOR MOTOR VEHICLES Filed Oct. 20, 1934 15 Sheets-Sheet 9 June 1, 1937. R. c, CLERK 2,082,332

GEAR CHANGING MECHANISM FOR MOTOR VEHICLES Filed Oct. 20, 1954 15 Sheefs-Sheet 1o 203272 6. (jerk June 1, 1937. R. c. CLERK GEAR CHANGING MECHANISM FOR MOTOR VEHICLES 15 Sheets-Sheet 12 Filed Oct. 20, 1934 June 1, 1937. R. c. CLERK GEAR CHANGING MECHANISM FOR MOTOR VEHICLES Filed Oct. 20, 1954 15 Sheets-Sheet 13 New Z; Mentor,-

June 1, 1937. 2 R, Q CLERK 2,082,382

GEAR CHANGING MECHANISM FOR MOTOR VEHICLES Fil t- 2 1934 15 Sheets-Sheet 14 Ir l/en for! 20 Jeri l. (fer/f June 1, 1937. 'R c CLERK 2,082,382

GEAR CHANGING MECHANISM FOR MOTOR VEHICLES Filed Oct. 20, 1934 15 Sheets-Sheet l5 Patented June 1, 1537 4 GEAR-CHANGING MECHANISM FOR MOTOR VEHICLES Robert Cecil Clerk, Kingston, Jamaica, British West Indies Application October 20, 1934, Serial No. 749,262

-In Great Britain October 20, 1933 25 Claims. (oi.19z-.o1)

This invention relates to gear-changing mech- Fig. 11 is still another view similar to Fig. 8 anism for motor vehicles and more particularly showing the valves in still another position; to mechanism of this kinclgfor use in vehicles Fig. 12 is a schematic perspective view similar having change-speed gears of the linear, to that shown in Figs, 1 and 7, but showing a 6 straight gate or 'preselecting self-changing type further modification of the gear-changing arand has for its object to render unnecessary 'rangemen't of this invention as applied to a the normal manual operation of the clutch, and, motor vehicle for ordinary road service, to effect in its fully automatic form, the gear-selecting the fully automatic selection and change of the lever. change-speed gears thereof; According to this invention provision is made Fig. 13 is a diagrammatic view showing one of 10 of gear-changing mechanism for use in motor the operative positions of the multiple series vehicles whereby the operation of the clutch and valves in the operation of this embodiment of change-speed gear changing means of thevethe invention; hicle is effected by a fluid pressure difierential' Fig. 14 is a view similar to Fig. 13 showing the 15 created by the passage of a fluid through mulvalves in another position; 15 tiple series valves which are selectively. con- Fig. 15 is another view similar to Fig. 13 showtrolled by, the movements of the accelerator 'ing the valves in another position; and/or brake-and/or gear changing means. Fig. 16 is still another view similar to Fig. 13

In order that the invention may clearly be showing, the valves in another position;

2 understood in its practical application several Fig- 17 is a furt r V ew similar to'Figh 13 constructional embodiments thereof will now be showing the Valves in another Position; described with reference to the accompanying Fig. 18 is a still further V w Similar to 13 drawings in which: showing the valves in another position;

Fig. 1 is a schematic view,-in perspective, of 19 is yet another view similar to 13 5 a semi-automatic arrangement of gear changing showing e Valves in another Position;

' mechanism according to the present invention 20 is an additional View similar t F 13 shown applied to the power unit of a motor ves g thevalves 1n r i i n; hicle which is provided with a manually operat- 21 is another. additional View similar to ed preselective change-speed gear mm, Fig. 13 showing the valves in another position;

Fig 2 is diagrammatic View showing one of Fig. 22 is a detail view drawn to a larger scale 30 the several operative positions of the multiple gear selecting mechanism forming P of 1 series valves which form an essential part of' the lastmentioned embodlment;

the gear changing mechanism of this invention; 23 issnothel detail view partly in sec- Fig, 3 is a View similar to 2 Showing the tion of a portion of the gear selectingvmechavalves in another position; nism: I

Fi 4 1 th r i il 't Fig 2 Show: Fig. 24 is a schematic perspective view similar ing the valves in still another position; to Figs. 1, 7, and 12 sh n a further fi a- Fig. 5is still another view 'similar to Fig. 2 tion of seer-changing mechanism of this showing the valves in another position; invention applied to the power unit of a motor Fig, 6 i a, detail vi w of a, portion f th vehicle to effect a substantially full automatic 40 mechanism; 1 selection and change of the change-speed gears Fig. 7 is a schematic perspective viewsimilar of the vehicle, while to Fig. 1 but showing a modification of the gear Fig. 25 is a diagrammatic view showing one of changing mechanism of this invention arranged the operative positions of the multiple series to effect the fully automatic selection and change valves in t Operation 0! his em iodiment of of the change-speed gears of a racing motor; v the invention.

Fig. 8 is a diagrammatic view showing one of 26 is a View similar to 25 showing the several operative positions of the multiple t e a s in another position; series valves in the operation of this embodi-' is another View similar to g 5 showment of the invention; ing the valves in another position; Fig, 9 is a view similar to Fig. 8 showing the Fig. 28 is still another view similar to Fig. 25 valves in another position; I showing the valves in another position;

Fig. 10 is another view similar to Fig. 8 show- Fig. 29 is a further view similar to Fig. 25'

ing the valves in another position; showing the'valves in another position;

Fig. is a still further view similar to Fig. 25 showing the valves in another position;

Fig. 31 is yet another view similar to Fig. 25 showing the valves in another position;

Fig. 32 is an additional'view similar to Fig. 25 showing the valves in another position;

Fig. 33 is another additional View similar to Fig. 25 showing the valves in another position; and

Fig. 34 is a further additional view similar to Fig. 25 showing the valves in another position.

In the following description similar references areused to indicate similar parts of the mechanism in the various embodiments of the invention.

To clarify the positioning of the valve slides in relation to the passages of the valve block in each of thediagrammatic figures of the draw-' ings numbered as above and hereinafter specifically referred to the valve block is represented by two juxtaposed sectional elevations the right hand section showing the vacuum passages and associated valve slides while the left hand section shows the air passages and associated valve Referring to Figs. 1-6, and more particularly to Fig. 1, the invention is shown applied to the change speed gears of a motor vehicle for the 7 purpose of effecting the gear changing operations in a semi-automatic manner. Shown in schematic perspective in Fig. l is the prime mover IU of the motor vehicle, comprising a multi-cylinder internal combustion engine which may be of any standard type. The crank shaft of the engine (not shown) drives a flywheel in the casing while a change-speed gear set and clutch meanshoused in a gearbox I2 are arranged to transmitthe engine driveto the propeller shaft Ha. In the present constructional example the gear set is of the ,pre-selective and power change type and since it forms no part of the present invention neither its arrangement within the gearbox l2 nor the principles' of its operation will herein be described. To this end reference may be had tothe'published description of any standard type of preselector gear which could be adapted to this purpose. The shaft l5 to which the rocker arm l5a is secured extends within the gearbox l2 to operate the indicated in Fig. -1.

- will by the driver of the vehicle.

gear pre-selector means, while a second shaft I9 to which is secured the rocker arm |9a extends within the gearbox l2 to operate the gearchange mechanism and the clutch or that which serves as a clutch in change-speed mechanism of this kind. Pre-selective gears of this kind normally are selected manually, as is the case in this arrangement, and usually through a-control I la mounted upon the steering wheel l8, the latter together with the steering column |8a being A, control rod serves to connect the control. Ila through a link It to the rocker arm |5a of the gear selector shaft l5 so that the selection of the gears accordi g to an index adjacent the control I'la can be ade at To effect the power gear change the gear change rocker arm |9a is linked to the piston rod 2|; of 'a servo motor 20 of the fluid pressure differential type,

- the cylinder of which is connected by the union hereinafter described. The valve block 50 is interposed between the fluid conveying pipe 29 and I a vacuum pipe 25 which is connected at one end to a vacuum reservoir 26. The reservoir 26 is "evacuated through a pipe 21 which is connected to the intake manifold 28 of the engine )0. The engine speed control in this arrangement comprises the usual accelerator pedal l3 pivotally mounted upon a shaft I31: and connected by the rod M to the throttle of a carbureter (not shown). I

The multiple series valves'for controlling the actuation of the servo motor 20 in this arrangement comprise passages formed in thc'valve block 50 which is secured to some part of the vehicle structure e. g. the engine side of the dash or instrument board (not shown). The valve block 50 is connected on one side thereof by means of the union 59, with the vacuum pipe 25 while the fluid delivery pipe 29, hereinafter known as the servo pipe, is connected to the opposite side of the valve block through the medium of the union 60. Juxtaposed vacuum passages 5|, 52, extending across the block 50 from the vacuum side to the servo side thereof are joined at one extremity by a cross passage 53, which communicates with the vacuum pipe 25 through the union 59 and short passage 59a. The further extremities of the vacuum passages 5|, 52, are joined by the cross passage 54:; to the passage 54 which communicates with the servo motonpipe 29 and union 60 through the short passage 50a. Juxtaposed air passages 55, 56, offset from the vacuum passages, also extend across the block 50 from the vacuum side to the servo side thereof. On the servo side of the block the passages, 55, 56 are joined by the cross passage 54 so as to communicate with the servo motor pipe 29 while the further extremities of the passages 55, 56-passthrough the appropriate side of the block and so lie open to the atmosphere.

The communication on the one hand between the servo pipe 29 and atmosphere through the air relief passages 55' and 5B, and on the other'hand between the servo pipe 29 and vacuum pipe 25 through the vacuum passages 5|, 52 is controlled by bifurcated ported valve slide plates 51, 58. Suitable guide slots are cut through the block 50 transversely of the valve passages to receive the slides 51a, 51b and 58a, 58b of the slide plates 51, 58 in such manner that the ported slides 51b, 58b each pass across both air relief passages 55, 56 while the ported slides 51a, 58 each pass across the vacuum passages 5|, 52 so that the communication between the connections of these passages is ininto register. The slide 5111 is provided with'an elongated slot or port 84 which is arranged to register in turn with'the vacuum passages 5|,

52; slide 51b has an elongated port Bland bleed ports 88, 89, the port 81 being arranged to register in turn with the air passages 55, 56. while the bleed ports 88, 89 in turn register with the air passage 55; slide 58a. is provided with two passage 56, and a slotted port 9| and bleed port 90 which in turn register with the passage 55.

The valve slide plate 51 is displaced in accordance with the movement of the accelerator pedal l3 through a linkage comprising the arm 8| secured to the plate 51 and a connecting rod 3| which is pivotally secured at its extremities to 7 p as the arm 6| and one arm of a bell crank rocking lever 40, the other arm of the latter being slotted to engage a pin 4| extending from a collar 4|a which is rigidly secured to the accelerator throttle rod l4. Thus in the longitudinal displace- -ment of the rod M the lever 40 is rocked to impart sliding movement to the valve slide 51.

The setting of the second valve slide plate 58 for each gear change is determined directly by the movement of the gear selector control |1a. as follows. A vertical, flanged slide member 63 slidably mounted in fixed guides 66 is formedat its extremities with abutments' 64, 65 which are bored to form bearing brackets'for a rod 61 which is longer than the member 63 and passes through the abutments 64, 65 as shown. The rod 61 which is thus normally positioned as shown is connected at its lower extremity with the rocking arm |5a through the rocking bell crank 36 and connecting rods 35, 35a. The rod 61 is centralized tothe slide 63 by means of two comparatively stiff helical compression springs 68, 69 which both embrace the rod so that their ad-. jacent extremities abut either side of a collar 10 secured to the rod 61 while their further extremities engage the inner faces of the abut- .ments 64, 65 respectively. By this arrangement the rod 61 is displaced in the movement of the gear selector shaft l5 and rocking arm |5a and with it is displaced the slide member 63 unless the movement of the latter is resisted by a force greater than the strength of the springs 68. 69.

The vertical edge of the flange 63a of the slide member 63 is formed with -a series of projections or teeth 63a, 63b, 63c, 63d, and 63a, all of which are of equal width and even pitch, 'the latter preferably being twice the width of the teeth plus a suitable tolerance. The proportions of the linkage 33, 36, 35a is carefully chosen so that ,the amplitude of movement of the rod 61 for each gear selection is equal to the pitch of the projections 63a63b. Moreover, the linkage as shown in Fig. l is arranged to move the slide member 63 and rod 61 upwards in the direction of the arrow 11. as shown in the drawings for changes up to higher ratio gears and downwards in the direction of the arrow d for changes down to gears of lower ratio. Thus the gap 63ab will correspond to neutral position of the gears,

gap 6317-0 to first gear, gap 63cd second gear, gap 63d-e third gear and below 63c top gear, while above 6341 will correspond. to reverse gear. The valve slide plate .58 carries an arm 62 to which is' pivotally secured a slotted lever 12.

The lower extremity of the lever 12 is formed with a projection or nose 13 which is arranged to register with and engage any of the gaps between the teeth or projections 63ae. As shown in Fig. 1 the nose 13 is engaging the gap 63b-c so that in this position of the' arrangement the which would be in first gear with the clutch engaged. One arm of a further rocking bell crank 16, which is pivotally mounted at 16a. adjacent which abuts the underface of thecollar 16 and the second collar 19rigidly secured to the rod 8|.

- The lower extremity of the rod 8| is pivotally linked with the gear change rocking arm |9a through the rocking bell crank 23' and connecting rod 22; Thus in the actuation of the clutch and gear change mechanism the lever 12 1s rocked outwardly away from the slide 63 so that the nose 13 disengages the teeth of the slide 63. The valve slide plate 58 normally is held in the position shown in Fig. 1 by thecentralizing heli cal tension springs 82, 83 which aresecured at their inner adjacent extremities to a pin extending rigidly from the arm 62, while their outer extremities are anchored tothe fixed projections The operation of. this embodiment of the invention will now be described with reference to Figs. 2 to 5 of the drawings'in which diagrams,

for clearness, the centralizing springs 82, 83 and,

pin 85 have been shown in a diflferent form. As above mentioned the position of the gear changing mechanism as shown in Fig. 1 indicates that the vehicle is in first gear with the clutch en-' gaged and the accelerator about to be further depressed and throttle'opened to speedor run up the engine preparatory to changing up to second gear. The opening ,of the throttle will move the valve slide plate 51 upwards in the direction of the arrow 0' while closing the throttle will move the valve slide in the opposite direction so that in running up the engine as above mentioned the valve slide plate 51 will move upwards from the position shown in Fig. 1 to that shown in Fig. 4 so that port 84 in slide 51a will be out of register with vacuum passage 52 but in register with passage 5| and port 88 in slide 51b in register with air passage 56. However the valve .slide plate 58 will be set as shown .in Fig. 1 with neither port 85, 86 in register with the vacuum passages 5|, 52 so that vacuum cannot pass to the servo motor 20, while at the same time the bleed port of slide 581) is in register with air passage 55 to ensure'that the servo motor remains inactive. If the driver intends to change up to second gear. he will continue to speed up the engine in first gear and pre-select second gear by moving the selection control |1a to second gear which will move the rocking arm |5a in clockwise direction and thus lift upwardly the rod 61 which will carry therewith the slidemember 63 to the position shown in Fig. 2. Through the engagement of the ,nose 13 of the rod 12 between the teeth 63a and 63b the valve slide plate 58 also will be moved upward to the position shown in Fig; 2. in which the port 85 of slide 58a. registers with vacuum passage 52 and port 86 of slida' 58a remains out understood that with the second gear pre-selected and the accelerator pedal depressed and throttle open to run up the engine speed the vacuum still remains cut off from the servo motor 20 while the air relief also is now out off. However, when the engine and vehicle reach the right speed for a good change up the driver releases the accelerator pedal to close the throttle as is normal road driving practice in changing up and thus the valve slide 51a is moved downwardsto the position shown in. Fig.

' '2. Port 84 in slide 510. now registers with vacuum passage 52 and thecylinder of the servo motor 20 is evacuated through pipe 29, ports 84,

85' in passage 52 and pipe 25. The servo motor 20 is thus energized to operate the clutch and gear changing mechanism through the rocking arm l9ct and rocking shaft l9 so that the speed gears are-changed to second speed.

The operative movement of gear changing mechanism rocks the bell crank 23 in clockwise direction so that the rod 8| is drawn downwards in turn to rock the bell crank 16 in clockwise.

direction about its pivot Ilia. Thus the lever 12 is moved outwards about its pivot '15 and the I ,bleed port98 in slide 5% registers with the air passage 55. Since the throttle remains closed during the gear changing operation port 81 in slide 5'"; also is in register with the air passage 55 so that the vacuum in the cylinder of the servo 28 is relieved by air flowing along the passage 55' through ports 81, 98 and then through pipe 29. The rate at which air enters the servo motor is controlled by the size of the bleed port 90 allowing sumcient time for the engine revolutions to drop to the required extent to ensure a smooth re-engagement of the clutch means in second gear. It will be understood that in the clutch .re-engagement the piston of the servo motor 20 will return to the v position shown in Fig. 1 which will normalize the lever I2 through the linkage described so that the nose 13 will again engage between two of the teeth of the ,member 63. Since the normal position of the tion of the next gear to be engaged. Further changes up to topgear may be made in a manner similar to that above described butif a higher gear ratio is pre-selected on the over-run of the engine, 1. e., with the throttle closed, the

gear change will follow immediately upon thesettlng of the preselection mechanism the change taking placeunostentatiously and smoothly.

When it is desired to change down to a lower gear ratio than that in which the vehicle is being driven the movements 01' the gear preselection echanism and thereiore-the valve slides a the associated controlling mechanism "are reversed. 'Assuming that the lower ratio gear is selected when the throttle is closed the change down to the selected gear will not occur until the accelerator is again pressed down to open the throttle. The movement of the manual control Ila to select a lower gear will rock the rocking bell crank I5 in anti-clockwise direction. which in turn will pullthe rods 35 and 61 downwards. The slide 63 thus will also be moved downwards carrying therewith the lever 13, arm 62 and valve slide 58 to the position shown in Fig. 4,-i. e. with port 86.01. slide 580 registering with vacuum passage 5| It the throttle is now opened the' valve slide plate 51 will be moved up to the position shown in Fig.- 4

so that port 84 of slide 51a also registers with vacuum passage 5| and the cylinder of the servo motor 28 is exhausted along the last mentioned passage through the registering ports, thus energizing the motor to eflect the clutch-disengage- 'ment and change-down oi. the gears. As above described the; valve slide plate as. will at once be centralized but in this instance by the spring 82 to assume the position shown in Fig. 5 so that the maximum displacement of the slide 83.

the degree of throttle opening sothat the engagement of the clutch or its equivalent, such as the appropriate brake bands of epicyclic gears if such are used, is regulated according to the engine speed and thus achieved with smoothness and ease.

If the change, down is being eilfected while braking so that by reason ,of the speed of the vehicle the slow clutch engagement is undesirable this operation may be varied by the driver as follows. down to the preselected gear effected as above described by opening the throttle, the latter is closed; the closing of. the throttle immediately after the gear change down, moves the valve slide plate 51 downwards sothat port 81 in slide 51b registers with the air relief passage 55 and the large port 9| in slide 58b which at this instant is still in register with passage 55 since the valve slide plate 58 has not yet been released to the upward pull of the spring 82.

Vacuum in the cylinder of the servo motor 20 opened which achieves the gear change as in the changing-down operations above described. When starting the vehicle from a standstill in neutral gear, first gear is preselected with the throttle partially open; releasing the throttle evacuates the servo motor 20 through ports 84, 85 along passage 52 to achieve the change to first speed gear and thethrottle is again opened to de-energize the servo motor by air 'relle! through bleed-port 89 and the overlap of port 92 along air passage 56.

The extent of the sliding movement 0! the valve slide plate 58 is limited by the pin 15 engaging the slot 14 of lever 12, the slot 14' being of such length that the displacement of the slide member 63 and consequently the lever 12 and valve slide plate'58 cannot be more in either direction than the pitch length oi the '.teeth of the member ,83. Thus if the selector control Ha is inadvertently displaced for a distance equal to two or more gear settings, the valve slide plate 58 can only be displaced the correct distance for the requisite valve setting, the springs 68,- 69 constituting a lost motion device in that one 01' these springs will compress and the other extend when the rod 81 overruns As. shown in Fig. 6, ii,- in changing up, the gear preselecting device is advanced two stages in the one movement the rod" will be moved upwards fora corresponding distance i.-e. twice the distance normal for a single change up step. The slide 83 and valve slide plate II will move with Immediately following the change the rod 61 until the lower end of the slot 14' encounters the pin I whereupon the slide 63,

lever 12 and valve slide plate 59 are halted selecting andself-changing mechanism and au-= tomatic clutch control according to the present invention for use in racing cars will now be described with reference to Figs. 7 to 11 of the accompanying drawings. Referring more particularly to Fig. 7, it will be seen that the essential components of the arrangement are similar to those described in reference to the first constructional embodiment and comprise the prime mover or power unit I9, fiywheel housing II, combined clutch and pro-selectiongear-set I2 and propeller shaft Ila, the gear-set and clutch being power operated by means of the servomotor 29 which is served by pipe 29 and connected through a multi-series valve block 59 and pipe 25 to a vacuum reservoir 29 which, in turn, is connected by pipe '2? to the inlet manifold of the power unit I9. In this arrangement the while the air passage 59, open at one extremity to the atmosphere, also communicates with the pipe 29 through the union 99. As in the first embodiment, two ported, bifurcated valve slide plates 5i, 58, are mounted in the block 59 so that the slides 91a, 99a intersect the vacuum passage SI while the slides 91b, 58b intersect theair relief passage 55. In this embodiment however, slide 91a is provided with a slot or elongated port H9, arranged to register with vacuum passage 9I, slide EBa is provided with two ports H4, H9, each of which registers in turn with vacuum passage 5|, slide 51b has ports I9I, H32, each of which registers in turn with air passage 95, while slide 98b has port I39 which registers with air passage 55. In this arrangement the direction of movement of the valve slide plate 51 is reversed, i. e. when the accelerator pedal I3 is depressed to open the throttle- (not shown)- the valve slide plate 51 .is moved .downwards in the direction of the arrow 0. To this end the rocking bell crank 49,.which is slotted to receive the pin 4| carried by the collar 4 I'a secured to the throttle rod I4, is faced about upon its pivot so that its response to the movement of the rod I4 is opposite to that of the first embodiment and the connecting rod 9I, linked to the arm 6|, is caused to pull the slide valve plate 51 downwards when the throttle is opened.

The arm 62 attached to the valve slide plate 98 extends downward and is shaped at its lower extremity irrthe form of a flat topped, wide faced cam 92a the face of which is associated with two cam follower levers 93, 94 which are pivotally mounted upon pivot pins 95, 96 respectively, so that their fixed extremitiesare closely adjacent. The cam-eng ingfaces 93a, 94a at the adjacent extremities of the levers 93, 94 are shaped in' a curvature substantially corresponding to the rise of the cam 92a and terminating in shoulders.

93b, 94b which are engaged by the cam. 92a in its displacement so that the levers 93, 94 in turn are rocked outwardly about their pivot pins 95, 96. The outer edges 93c, 94a of the levers 93, 94 are inclined inwardly towards the free extremities of the levers so that when the shoulder 93b and 94b rides up upon the cam face 62a and the corresponding lever is rocked outwards, e. g., the lever 94 as shown in fulllines in Fig. '7, the in-' clined edge 940, as shown, liesparallel with the longitudinal edges of the lever 62 for a purpose hereinafter described.

Parallel with the arm 62 and adjacent thereto is slidably mounted in guides (not shown) a gear selecting rod I92 which is secured at its lower crank 23 to the gear selecting rocker arm I5a of the gear set I2. The rod I92 carries teeth or projections I92a-f which project towards the plane in which'lie the levers 93, 94, the edges of the teeth being square out while the upper faceof the tooth I92b and under face of the tooth I92e are ramped for a purpose hereinafter described. A pair of levers 98, 99 mounted upon a fixed pivot 91 and normally held closed by a helical tension spring 91a applied to adjacent extremities thereof are positioned so that the further extremi-v ties of the levers which are bent to provide fingersv 99a, 99a. lie between the arm 62 and gear selecting rod I92 and beyond the plane of the teeth of the latter member and the cam follower levers 99, 99. Pawl members in the form of short bars I99, I9I which extend from the rod I 92 to the levers 99, 99' are pivotally mounted upon the levers 99, 99, respectively by means of short arms I99a, I9Iu, the latter being pivoted at the base of the fingers 98a, 99a. Compression springs I991), IBIb interposed between the finger 99a and pawl I99 and finger 99a and pawl I9I urge these members towards, th teeth on the rod I92, the

i= arrangement being uch that the pawls, I99, I95

are each permitted to engage the teeth of the lever 99 is shown in'tlie same figure of the drawings. The piston of the servo motor 29 is connected to the levers 98, -99 by the cable I93 so that in .the'gear-changing and clutch-disengaging movement these levers are spread apart in the manner of a pair of scissors by a pull on the cable I93 whereupon the spri loaded pawl members I99, I!" move in 'oppo ite directions; 1. e., down and up respectively. If the arm 62 is moved downwardly so that its cammed extremity rocks lever 94-outwards and permits lever 93 to move inwards as shown in full lines-1n Fig. '7 the falling pawl I99 will be deflected by the edge 940 of the lever 94 and thus ride over the tooth or projection I92d while the ris- "ing pawl ,I9I, undeflected by the inwardly reclining lever 93, will fall behind the tooth I92c the upper face of tobth I92d so that the rod I92 is moved down to select a lower gear ratio through the linkage above. mentioned. The 

